Microparticles in the nanometer and micrometer range apparently exhibit quantal properties inherent to materials of such size, the surface-to-volume ratio thereof is significantly larger than that of a smooth substrate or the like, and the surface condition thereof is highly active. For these reasons, such microparticles have drawn attention as functional materials having optical, electronic, vital, and other functions.
If nano-sized microparticles could be produced with the use of materials composed of two or more different components having different properties, and in particular, two or more properties could be imparted to a single microparticle and the application range thereof could be further expanded.
As techniques for producing microparticles comprising a material composed of two or more different components, attempts to apply microparticles to an adequate substrate and coat the same with metal via sputtering or other means and attempts to synthesize a polymer brush on the surface to prepare asymmetric microparticles (Janus microparticles) have been made (Non-patent Document 1). In addition, attempts to bind polystyrene microparticles to silica particles with the use of an emulsion to prepare dumbbell-shaped microparticles and attempts to synthesize polymer brushes have been made (Non-patent Document 2). These techniques, however, are disadvantageous in that they require many steps and offer low productivity.
A method referred to as “seed polymerization” is known as a method of forming asymmetric and irregular-shaped microparticles (Patent Document 1). However, this method is disadvantageous in that it requires a complicated procedure, one of the two types of polymers used is always positioned on the microparticle surfaces, and the orientation among polymers in the microparticles is significantly limited.
As a method for producing microparticles comprising polymers based on principles different from those of the aforementioned methods, a method has been reported in which a single organic material, such as a homopolymer or block copolymer, is used, a poor solvent made of the aforementioned material compatible with a good solvent is added to a solution of an organic material dissolved in a good solvent to lower the concentration of the material, and microparticles comprising the organic material are prepared ((Patent Document 2, and Non-patent Document 3). In addition, a method for producing microparticles with the use of an organic material composed of two or more different components has been reported (Patent Document 3).